Selecting ELIN for Multiple Calls within Same ERL
The device supports the receipt of up to five ELIN numbers in the XML message of each incoming SIP INVITE message. As discussed in the preceding sections, the device sends the ELIN number as the E9-1-1 calling number to the emergency service provider. If the XML message contains more than one ELIN number, the device chooses the ELIN according to the following logic:
| ■ | If the first ELIN in the list is not being used by other active calls, it chooses this ELIN. |
| ■ | If the first ELIN in the list is being used by another active call, the device skips to the next ELIN in the list, and so on until it finds an ELIN that is not being used and sends this ELIN. |
| ■ | If all the ELINs in the list are in use by active calls, the device selects the ELIN number as follows: |
| a. | The ELIN with the lowest count (i.e., lowest number of active calls currently using this ELIN). |
| b. | If the count between ELINs is identical, the device selects the ELIN with the greatest amount of time passed since the original E9-1-1 call using this ELIN was terminated with the PSAP. For example, if E9-1-1 caller using ELIN 4257275678 was terminated at 11:01 and E9-1-1 caller using ELIN 4257275670 was terminated at 11:03, then the device selects ELIN 4257275678. |
In this scenario, multiple E9-1-1 calls are sent with the same ELIN.